Reproductive carrier screening panel (CF, SMA and fragile X)
Reproductive - Carrier screen
Use of test
Carriers of cystic fibrosis (CF), spinal muscular atrophy (SMA) and fragile X syndrome (FXS) are common in the Australian population. Approximately 1 in 16 people is a carrier of one or more of these conditions. Most carriers do not have a family history of relatives affected by the disorder and are unaware that they are carriers. Approximately 1 in 160 Australian couples will be found to have a one in four chance of having a child with one of these three conditions.
Current RANZCOG guidelines recommend that screening for common genetic disorders, including CF, SMA and FXS, be offered to all women prior to pregnancy.
The result provided will indicate whether a mutation was found, and the implication for the patient.
Carrier for CF or SMA: individual is at increased risk of having affected children. Genetic counselling and testing of reproductive partner is recommended.
Carrier for FXS Females: individual is at increased risk of having affected children. This result also has potential medical implications for the individual being tested. Genetic counselling is recommended.
Carrier for FXS Males: carrier testing of males should be considered carefully. Male mutation carriers are not considered to be at risk of having children with FXS; however their daughters will inherit a premutation and be at risk of having affected children themselves. This result also has potential medical implications for the individual being tested. Genetic counselling is recommended.
Carrier status for CF, SMA and FXS unlikely: a mutation was not detected but the possibility that the patient is a carrier cannot be excluded.
Note that carrier testing for FXS in males is not routinely performed as part of the reproductive carrier screen. Unaffected men with a mutation are not at risk of having children with FXS; however their daughters will inherit a premutation and be at risk of having affected children themselves. Unaffected male carriers are also at risk of developing a neurodegenerative condition in later life (fragile X-associated tremor/ataxia syndrome). This testing can be provided on specific request, if indicated on the basis of family history or clinical features. Due to the predictive nature of the test in this scenario, genetic counselling is recommended.
It is important to understand no preconception carrier screen is able to detect every mutation that causes CF, SMA and FXS, nor will it identify carriers of other genetic conditions. Therefore, a “no mutation” result does not eliminate the risk to the patient of having a child affected with a genetic disorder.
Our clinical and scientific experts have selected the most common mutations and best technology available to detect the vast majority the relevant mutations for these three most common inherited conditions.
Depending on the results provided, referral for genetic counselling and discussion of reproductive options may be appropriate. A list of private and public providers of clinical genetics and genetic counselling services is available here. For couples who are identified as being at high risk (25%) of having an affected child, Sonic Genetics offers free genetic counselling.
This is an assay for heritable mutations. It may raise issues of ethics or consent that are different from most other investigations ordered in the routine care of a patient. The consent form is not mandated, but could be used to guide the discussion with the patient.
In the case of carrier testing of an unaffected child, national regulations require that the laboratory has evidence of pre-test counselling by a genetics professional and written consent.
CFTR: Analysis of the CFTR gene for 50 common mutations (including the 5T variant).
SMA: Copy number analysis of the SMN1 gene by MLPA.
FXS: The mutation in this gene is abnormal repetition (or expansion) in the DNA sequence.
Requesting the test
This test can be requested by any medical practitioner.
4 mL blood in EDTA (separate tube required). Specimens may be collected by the requesting practitioner or at any Sonic Healthcare collection centre (see link below).
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We recommend that the patient or another adult check the labelling of request forms and sample tubes.
Please note whether or not the patient has a family history of CF, FXS or SMA on the referral form. If there is a family history, please provide as much information as possible about the family pedigree and any previous testing with results (if available) that has been performed for other family members.
10 business days.
If a female is tested first and found to be a carrier of either cystic fibrosis or spinal muscular atrophy, a free of charge test of the relevant gene will be offered to her partner (full details will accompany the test report).
As a screening test in the general population, this test is not rebated by Medicare. The laboratory assumes that the patient or client has provided informed financial consent for the test.
There are Medicare items for carrier screening for FXS and CFTR under specific circumstances, and these may cover part or all of the cost of this screening panel. Please note that, with one exception (see below*), the Medicare rebates for CFTR carrier screening are only available for test requests from a medical specialist or consultant physician. Please contact the laboratory for further information.